From U.S. Pat. No. 4,634,780, it is known that lactones having a 5 or 6 membered ring can be prepared by reacting, inter alia, an alkenol containing 5 or more aliphatic carbon atoms with carbon monoxide. However, the following restriction is made with respect to the alkenols which may be used in the process: the olefinic unsaturation should not be located more than three carbon atoms from the hydroxy substituent. Said patent specification does not teach in any way the conversion of alkenols having 5 or more aliphatic carbon atoms in which the aliphatic unsaturation is more than 3 carbon atoms removed from the hydroxy substituent. Moreover the process described in said patent specification should be carried out in the presence of oxygen in order to obtain acceptable, yet moderate, product yields. The catalytic system used in this reaction consists of: a protonic acid, one or more metals selected from the group consisting of palladium, rhodium, ruthenium, iridium cobalt or compounds thereof, and one or more metals selected from the group consisting of copper, molybdenum and iron.
It will be appreciated that the before-mentioned process has several unfavorable characteristics i.e. as starting compounds only alkenols can be used which have the olefinic unsaturation no more than three carbon atoms removed from the hydroxy substituent and a complex catalyst system is used.
Consequently, due to an increasing demand for lactone products which can be used as solvents and useful intermediates for chemical synthesis, there is a big need for a more universal and economical production process.
It has now been found that substituted or unsubstituted lactones having four or five carbon atoms in the ring can be produced with improved selectivity and improved yields by reaction of substituted or unsubstituted alkenols, in which the hydroxy group is 5 or more carbon atoms remote from the double bond, in the presence of a relatively simple catalytic system which is believed to cause isomerization in situ by shifting the carbon to carbon double bond of an alkenol, in which the olefinic unsaturation is more than three carbon atoms removed from the hydroxy substituent, to an alkenol in which the olefinic unsaturation is three carbon atoms removed from the hydroxy substituent.